The present invention relates to a method for controlling the automatic transmission in a motor vehicle having an engine, wheels, a wheel slip control system and an automatic transmission having a clutch.
In a vehicle having automatic transmission, certain roadway conditions can lead to less than optimal performance of the automatic transmission during gear shifting. For one example, icy, wet, or otherwise slippery road surfaces may result in wheel slippage immediately following a gear change. When shifting up on a slippery surface, there is a danger of wheel slippage in the positive direction (drive slip). Also, when downshifting on a slippery road surface, there is a danger of wheel slippage in the negative direction (brake slip).
Another example of less than optimal performance of the automatic transmission during gear shifting occurs when starting the vehicle from rest in conditions where there is a high resistance to travel, e.g. a steep roadway inclination, deep snow, etc. When the vehicle begins to move from rest, the automatic transmission is in the start mode, and thus it allows the clutch to slip until a certain minimum vehicle speed is obtained. In situations where there is a high resistance to vehicle travel, such as when the vehicle is on an upward incline or in deep snow, the vehicle usually takes longer to reach the minimum vehicle speed leading to a heat load and faster wear of the clutch. In some circumstances it can lead to permanent damage to the clutch.